I don’t feel so bad about the Nikon D2X and Nikon D200 focus precision problems after suffering through the Canon EOS 5D and 85mm/f1.2L today. Here are a few examples of why shooting a fast lens with a high resolution camera requires pinpoint focus—often impossible with autofocus due to its ambiguous coverage, and also impossible with manual focus with less than outstanding eyesight.
I placed the focus sensor precisely on the eye, but got sharp eyebrows instead:
Here I placed the focus sensor precisely on the shiny nut, but the EOS 5D focused a good 6 inches in front of it:
Perhaps I’m expecting too much, but I’d like at least one focus sensor that works. Such focusing errors reduce the success rate by 90% when shooting at f1.2 or f1.4. I haven’t yet checked to see if the Canon EOS 1Ds Mark II suffers the same problem; I carried the 5D for its lighter weight today.